A purple block after the halfway point flag leads to a room with two Koopas. Kill the Koopas to reveal the Green Star. After you blast through the long clear pipe, jump on the ? blocks to discover ...

A purple block after the halfway point flag leads to a room with two Koopas. Kill the Koopas to reveal the Green Star. The final Green Star is in a stack of Goombas near the exit pipe. Use a Koopa ...